1. Field of the Invention
The present invention relates generally to optical character recognition apparatus and, more particularly, to an optical character recognition apparatus suitable for recognizing, for example, a character of a printing document so that a recognized character is converted into a character code.
2. Description of the Prior Art
In order to automate a process in which an operator selects types, for example, in the type printing, a character recognition apparatus is needed, in which respective characters on the original document are recognized and converted into character codes.
FIG. 1 shows a schematic arrangement of a conventional character recognition apparatus which is described in Japanese Patent Laid-Open Gazette No. 62-74181.
In FIG. 1, reference numeral 1 designates an original document reading section, and an original character signal S1 corresponding to light and shade of one page amount of the original document is supplied from this original document reading section 1 to a character string slice section 2. While this original character signal S1 is formed by analyzing the original document by a predetermined density at every dot to thereby express a black dot in a high level "1" and to express a white dot in a low level "0", it is frequently observed that concentrations of respective dots are expressed by a binary number of a plurality of bits.
The character string slice circuit 2 is comprised of a first stage preprocessing section 3, a second stage preprocessing section 4 and a third stage preprocessing section 5. The original character signal S1 is preprocessed by the first stage preprocessing section 3 so that a noise thereof is removed and that the original document is rotated and corrected. In the second state preprocessing section 4, a character area AR (see FIG. 2) is distinguished from other areas (areas of photograph, drawing and so on) and only image data involved in that character area AR is extracted. In the third stage preprocessing section 5, a character string signal S4 corresponding to character strings AR1, AR2, . . . involved in the character area AR extracted is extracted.
In order to extract the character string S4, as shown in FIG. 2, the position of each dot in the character area AR is expressed by (X, Y) coordinates in which an X axis is presented in the horizontal direction and a Y axis is presented in the vertical direction. Then, values of "1" or "0" of respective dots are projected onto the Y axis and summed to thereby generate a Y projection signal Sy. Then, if this Y projection signal Sy is converted into a binary value by a predetermined threshold level, intervals of high level "1" of the binary-converted-signals are made corresponding with the character strings AR1, AR2, . . . and the character string signal S4 is supplied to a succeeding character slice section 6.
In the character slice section 6, a character string signal S4 of i'th character string ARi shown, for example, in FIG. 3A is projected onto the X axis to thereby generate an X projection signal Sx, and a coarse slice signal DT1 (see FIG. 3C) is obtained by converting the X projection signal Sx into a binary signal by a threshold value TH1 of the minimum level (value is 1). Then, a fine slice signal DT2 (see FIG. 3E) is obtained by converting this X projection signal Sx by a threshold value TH2 (see FIG. 3D) of an intermediate level. In a similar fashion, by generating the Y projection signals Sy during the intervals in which the fine slice signal DT1 is at high level "1", it is possible to generate a slice signal of the Y direction. Finally, as shown in FIG. 3A, with respect to, for example, a character [ ], a slice signal which goes high level "1" in the inside of the circumscribed frame 9 circumscribing this character from its outside is obtained, and with respect to a separate character [ ], a slice signal which goes high level "1" in the inside of circumscribed frames 11 and 12 circumscribing respective separate portions from their outsides is obtained. Then, a fundamental square slice character signal S7 is obtained by sequentially slicing only the portion in which the slice signal goes high level "1" from the input character string signal S4.
The fine slice signal DT2 of FIG. 3E is used to check a more detail structure of each character. Further, with respect to the separate character [ ] of FIG. 3A, there are provided two circumscribed frames 11 and 12, which must be synthesized in the later character recognition step.
Referring back to FIG. 1, a character recognition section 7 is shown to receive the fundamental square slice signal S7 at every circumscribed frames to thereby perform the character recognition. More specifically, the pattern matching processing is performed by utilizing characters (['], ["], [.degree.], etc.) existing in the range of upper half portion of the character string ARi of FIG. 3A and characters ([.degree.], [.degree.], [, ], etc. existing in lower half portion thereof as the first characteristic characters and corresponding character codes (JIS (Japanese industrial standards) codes and so on) are given to the character string ARi. If the character cannot be recognized by the above processing, then the character string ARi is categorized by an aspect ratio, h/w and a relative size where w is the width of the circumscribed frame and h is the height thereof. More specifically, the character is classified by determining whether the aspect ratio h/w falls in a range of 0&lt;h/w&lt;0.5 or in a range of 1.5&lt;h/w. Further, the character is classified by determining whether a longitudinal relative ratio h/h.sub.R and a lateral relative ratio w/w.sub.R fall in a range of 0&lt;h/h.sub.R &lt;0.5 and in a range of 0&lt;w/w.sub.R &lt;0.5 where w.sub.R is the width of the circumscribed frame of average size and h.sub.R is the height thereof, respectively. Then, the pattern matching processing is performed by utilizing characters lying in the above-mentioned ranges as the second characteristic character.
Characters, which are not categorized as the first and second characteristic characters, are processed by the pattern matching system with the dot patterns individually stored. If a predetermined coincidence is obtained, then that character code is given to the character. If characters, which cannot be recognized by the above processings, remain, an operation in which the circumscribed frame is further separated into a plurality of minute circumscribed frames and the operation in which these minute circumscribed frames are synthesized with the following circumscribed frame are executed. Incidentally, if a character, which cannot be recognized finally, remains, a reject code indicating that the character is a character which cannot be recognized, is assigned to that character.
Character codes of one page of the original document which are generated by the character recognition section 7 are stored in a predetermined memory apparatus together with informations indicating the position and size of the character.
Further, in order for the operator to determine whether or not the recognized result is correct, a video signal of character corresponding to that character code is supplied to a display section 8, such as a cathode ray tube (CRT) or the like. As a consequence, a group of characters are displayed on the display screen of the display section 8 as recognized results in the system corresponding to the original document. In that case, a square blank of high brightness is displayed on the portion of the character that cannot be recognized. Accordingly, if there exist the correction target character and the character which cannot be recognized, then the operator can typewrite a desired character in that portion in the same manner as that of the word processor.
As described above, the original character signal S1 corresponding to the light and shade of the original document is generated, this original character signal S1 is sliced by the circumscribed frame circumscribing one character to thereby generate the slice character signal S7 and the character corresponding to this slice character signal S7 is specified. Heretofore, it can be said that the above-mentioned character recognition algorithm itself is fundamentally established.
However, there arise various disadvantages from a manipulation standpoint when the operator operates this optical character recognition apparatus using such character recognition algorithm at office in actual practice.
One of such disadvantages is that it is very cumbersome to correct a character which is provided as a result of recognition. More specifically, while the character, which cannot be recognized, is displayed as a blank portion in the conventional character recognition apparatus, the original document must be copied beforehand or the original document must be picked up from the original document reading out section 1, each of which work is cumbersome for the operator because the character, which cannot be recognized and displayed as the blank portion, cannot be confirmed without consulting the original document in actual practice.
In order to remove such disadvantages, it is proposed to display an original document dot pattern corresponding to correction target characters (including characters which cannot be recognized). In that case, although only the dot pattern of the correction target character is displayed, if a separate character is extracted and recognized erroneously, there is then the disadvantage that the entire shape of the separate character printed on the original document cannot be predicted from the dot pattern of one portion of the separate character only.
Further, if the optical character recognition apparatus erroneously recognizes words [ ] on the original document as [ ] and displays the same, it is frequently observed that the operator cannot determine whether the word on the original document is [ ] or [ ]. At that time, even when only the dot pattern of the character [ ] the original document and which corresponds with the displayed character [ ] is displayed, the operator cannot determine whether or not the word on the document is really the word [ ].